Depolarization properties of metal space frame radomes for use in satellite communication systems

Radomes have traditionally only been used in military satellite systems. However, higher availability civil applications are demanding their consideration in the higher frequency bands and for dualpolarization frequency re-use systems. This paper investigates the depolarization performance of metal space frame radomes and presents results of XPD for radome covered antennas in the 4/6 and 11/14 GHz bands and for antennas of 30, 11, 5 and 3 m diameters. It is demonstrated that current polarization specifications adopted in the INTELSAT system should be able to be met by radome covered earth-stations using conventional antennas.     

Standardization on performance objectives of satellite systems using adaptive coding and modulation

The radiocommunication part of the International Telecommunication Union (ITU‐R) establishes the standards for wireless communications. Recommendation ITU‐R S.1062 specifies the performance objectives for satellite communication systems providing constant bit rate service. However, this is not applicable to most modern satellite communication systems utilizing adaptive coding and modulation (ACM) schemes to compensate for channel impairments, especially for systems operating in high frequency bands. For this reason, ITU‐R recently developed Recommendation ITU‐R S.2131 that is suitable for satellite systems with ACM. The developed Recommendation provides a method to determine performance objectives for satellite systems using ACM. Two possible objective parameters are presented, including packet error rate and spectral efficiency. This paper presents the standardization process, and the background used to establish new performance objectives. In addition, interpretations of the objectives are given by using estimation results for two different propagation characteristics.     

Code design for adaptive coding and modulation indicator in broadcast systems

In this paper, we address the coding problem for adaptive coding and modulator indicators in communication systems where users are divided into several classes according to their channel quality. Two novel methods are described to construct codebooks with variable length codewords forsuch an application. The proposed constructions satisfy all constraints of the system model, showing considerable gain in both the maximal and average length of codebook with respect to the current state of the art. The methodology includes a systematic way for constructing variable length codebooks where codewords are not uniformly distributed in the space, and thus, some codewords are more protected than others. The proposed construction can be easily adapted, by zero padding, to obtain a fixed block‐length code, with length equal to the maximal length of the designed variable‐length code but still smaller than that of the best state‐of‐the‐art code. Copyright © 2015 John Wiley & Sons, Ltd.     

空时分组码通信中的一类ICA盲检测方案

空时分组码（STBC）通过使用发射分集策略和空时编码方案可以明显改善系统性能。然而，其接收端必须获得准确的信道状态信息（CSI）才能进行有效的信号检测。而对于复杂的无线通信环境，这种前提条件有时却难以得到满足。独立分量分析（ICA）是一种将一个复杂的数据集合分解为多个独立子集的盲源分离（BSS）技术。通常情况下，即使没有空间信道的任何信息，ICA也可以仅凭接收信号恢复出发射信号。提出了一种利用ICA技术的STBC盲信号检测方案，在建立了适用于ICA的特定通信系统模型后，几种典型的ICA算法被用来进行性能比较。理论分析表明，ICA盲接收技术的应用可以在一定程度上替代基于信道估计的传统方法，增强系统对信道估计错误的顽健性。仿真实验结合了具体的STBC系统，比较了基于ICA的不同方案的性能，并讨论了最优的信号检测方案。     

On the design considerations of solid-state power amplifiers for satellite communications: A systems perspective

Conventional solid-state power amplifier (SSPA) design approach isolates radio frequency (RF) design from communication theory. In this paper, a unified SSPA design approach is proposed, which optimizes SSPA parameters (bias voltage and input RF signal power) to minimize total DC power consumption while satisfying received SNR constraint specified by the link budget. The effect of SSPA nonlinearity is quantified by the error vector magnitude measured at its output and the corresponding received SNR degradation is analyzed. Using the quantitative metrics for received SNR, it is possible to evaluate highly nonlinear SSPA classes such as Class-B or deep-Class AB, which are normally not considered in conventional SSPA design approach to be used in satellite communication applications.     

Voice transmission quality of mobile satellite communications systems

Recently, a number of commercial digital mobile satellite communications systems have become operational, and the introduction of more systems is imminent. The voice transmission quality of the Inmarsat-aeronautical, Inmarsat-M and Inmarsat-B systems was evaluated and compared with the quality of the Inmarsat-A analogue communication system on the basis of subjective listener opinion assessments. From this evaluation it can be concluded that, under nominal operating conditions, the current generation of digital mobile systems may offer a perceived performance that surpasses that of the older Inmarsat-A analogue system, at least when measured in terms of transmission quality.     

短波通信多组空时编码中等效MIMO模型ZF解码

面向短波通信提出了多组空时编码( MGSTC )的一种等效多输入多输出( MIMO )模型迫零( ZF)解码算法。该算法以降低运算复杂度为目的,将原多时隙MIMO系统拆分为多个多时隙单输入多输出( SIMO)系统并分别等效为多个新的单时隙MIMO系统模型,通过各自左乘等效信道矩阵的共轭转置后进行最大比合并( MRC)以及ZF解码获得发送信号估计值,避免了球形解码( SD)中对高阶矩阵的QR分解。仿真结果表明,与虚拟MIMO模型SD解码算法相比,等效MIMO模型ZF解码算法在误码率( BER)性能1 dB损耗的情况下,运算量降低一个数量级以上。     

Integration of satellite and terrestrial systems in future multimedia communications

In this article we examine the role of satellite communications in future telecommunication networks and service provision. Lessons from the past indicate that satellites are successful as a result of their wide area coverage or speed to market for new services. Niche areas such as coverage of air and sea will persist, but for land masses convergence of fixed, mobile, and broadcasting will dictate that the only way forward for satellites is in an integrated format with terrestrial systems. We outline future ways forward for satellites, and discuss the research challenges and technology advances needed to facilitate this integrated approach.     

通信卫星星座优化设计综述

通信卫星星座优化设计是构建通信星座系统的关键环节。对通信卫星星座设计中的优化模型和优化算法进行了综述和展望。首先,建立了通信卫星星座设计的一般优化模型;然后,从覆盖性能、星间链路和系统成本三个方面对优化模型中优化变量、目标函数和约束条件的构建进行了综述;之后,介绍了卫星星座设计中常用的三大类多目标优化算法,归纳总结了4种主流算法的主要特征,并比较分析了它们应用于卫星星座设计的优缺点;最后,指出了现有通信卫星星座优化设计中存在的问题及发展趋势。     

Content-based group-of-picture size control in distributed video coding

Controlling the group of picture (GOP) size in distributed video coding (DVC) is a difficult but important task since it has a direct impact on the coding performance. This paper presents a framework to adaptively control the size of GOPs in a Wyner–Ziv encoder by means of encoder-side decisions based on support vector machines (SVM) that uses simple features extracted from the original video content. To train the SVM, firstly this work proposes how to compute the sequence of GOP sizes with the best rate-distortion performance given the set of GOP sizes that can be used during the encoding process. Then, an algorithm based on the previously trained SVMs is presented to control the actual GOP size each time a new decision can be taken at the encoder. Results show that the proposed algorithm can achieve a rate distortion performance close to the ideal one. Moreover, comparisons with a reference adaptive GOP size selection algorithm in the literature shows gains up to 2 dB PSNR in the best conditions.     

Architecture and networking issues in satellite systems for personal communications

The paper expands on some specific aspects of personal communications via satellite, often–although not necessarily–envisaging extensive use of ‘small’ satellites, using orbits not necessarily coinciding with the geostationary one (36,000 km), but rather at 1000–11,000 km altitude. One key point to be borne in mind is the issue of internetworking between satellite and terrestrial systems. Network integration should be carefully implemented in order to comply with ITU future public land mobile telecommunication systems (FPLMTS) requirements, also accepted in the European Telecommunication Standards Institute (ETSI) universal mobile telecommunication systems (UMTS). In addition to some insight into the technology of small satellites and associated orbits, architectures and networking aspects of most relevant systems providing personal communication services (PCS) are addressed in some detail, and potential applications highlighted. Frequency spectrum allocation is addressed in the light of the 1992 World Administrative Radio Conference (WARC-92), taking into account also multiple access problems and regulatory issues such as Federal Communications Commission (FCC) licensing and spectrum sharing debates. Some remarks on critical technologies and cost conclude the paper.     

异步卫星协同通信系统中的双采样差分空时编码方案

针对双卫星中继协作通信系统中存在非符号周期整数倍的时延差问题,提出了一种双采样的差分空时正交频分复用（D-OFDM2）方案。所提方案在卫星信道条件未知的情况下,基于具有时延容忍的 D-OFDM编码,在接收端构造了一种双采样方法。该方法在以符号速率采样的同时,对当前主瓣大于相邻旁瓣的区间内增加一次采样,并将两次采样结果等增益合并。仿真结果表明,在系统时延差为非符号周期整数倍的情况下,该方法较单采样方法能获得更高的接收信噪比,同时改善了系统误码性能。     

Method of increasing the efficiency of coding communications systems with information feedback

A method of increasing the efficiency of the coding communications systems with information feedback is suggested. The operational logic of such systems is described followed by general formulas used to determine the error probability, average energy consumption and average number of iterations. The essence of this method lies in the appropriate and controlled choice of thresholds in the feedback channel receiver. This method of processing the code combinations in the feedback channel allows escaping energy losses under small signal-to-noise ratios in the feedback channel and increasing the system’s efficiency in the remaining cases. The technical realization of the suggested method is presented.     

The design of the mechanically despun antenna for the Intelsat III communications satellite

The use of a spin-stabilized communications satellite of large channel capacity requires a high-gain antenna which may be despun, mechanically or electronically, with respect to the satellite. The design of a mechanically despun antenna system for the Intelsat-III communications satellite is discussed. The communications signals utilize a high-gain directive antenna which is mechanically despun while an omnidirectional antenna is used for the telemetry information. Positional control of the directional antenna is provided by the control electronics subsystem such that the antenna is always pointed directly at the earth. Satellite-borne infrared earth sensors provide earth reference pulses to the control electronic subsystem for antenna despin stabilization and pointing. Also discussed is the bearing and lubrication system for the antenna drive assembly. In-orbit performance of the two systems launched is also given.     

差错控制对数字通信系统的可靠性的影响

通过对数字通信的各种信道编码方式、差错控制的类型以及差错控制编码分类的总结和分析,根据各种常用信道编码的比特差错率和码字差错率之间关系的差异,得出了差错控制编码对数字通信系统可靠性影响的定量计算结果,并用MATLAB仿真软件进行了分析和比较.又根据差错性能和信号带宽、信噪比、传输速率之间的关系,得出了评价干扰数字通信系统等级的一些想法,为进一步研究数字通信系统干扰效果的评估准则做一个理论基础.     

Optimized layered multicast with superposition coding in cellular systems

We consider the problem of optimal power allocation and optimal user selection in a layered multicast transmission over quasi‐static Rayleigh fading channels. A scheme based on superposition coding is proposed in which basic multicast streams and enhanced multicast streams are superimposed and transmitted by a base station, while users with worse channel conditions can only decode basic multicast streams, and users with better channel conditions can decode both basic and enhanced multicast streams. In this paper, subject to fixed user selection ratios, the optimal power allocation for each stream that maximizes average throughput is investigated, and the impact of power allocation on average outage probability is discussed. Finally, subject to fixed transmit power and power allocation, the optimal user selection ratio for enhanced multicast streams is also studied. Numerical results show that the optimized layered multicast scheme outperforms the conventional multicast scheme in terms of average throughput. Copyright © 2010 John Wiley & Sons, Ltd.     

Space-time coding scheme for the paired weak user in MIMO-NOMA systems

In view of the paired weak user’s poor outage performance in multiple-input multiple-output non-orthogonal multiple access (MIMO-NOMA) systems,Alamouti code was adopted to encode for the weak user in order to improve its outage performance by means of diversity,and the closed-form expression of the strong user’s ergodic capacity as well as the boundary-form expressions of the weak user’s ergodic capacity and outage probability was derived in the proposed model.Moreover,a power allocation algorithm for optimizing the system’s throughput was proposed.Finally,the numerical results show the accuracy of the derived expressions,the efficacy of the proposed algorithm,and that the weak user’s outage performance in the proposed coding scheme is far superior to that in the current coding scheme only adopting vertical Bell lab layered space-time (V-BLAST) code.     

多接口视频编码方案的设计与实现

针对现有编码系统处理视频格式单一的问题,提出多接口视频编码方案,采用TI DSP(TMS320DM8168)+FPGA构架,将多种常见的视频接口设计在同一系统中,应用FPGA采集视频数据后传送给DM8168,通过软件控制送至各子模块,进行编码。经长期测试结果表明,该系统编码性良好,视频显示无误码,适用性和通用性更强。     

高重频激光对不同编码体制的干扰效果研究

针对高重频激光干扰与不同激光编码之间关系的研究不够深入这一问题,采用归一化互相关函数法,量化分析了高重频激光干扰在搜索识别阶段对不同编码体制的干扰效果。仿真结果表明,高重频激光对不同编码体制的干扰效果存在差异;重复频率高于120kHz时,对所有编码体制的干扰概率几乎均为100%,各编码体制间无明显差别。